Yarn guiding apparatus

ABSTRACT

In the particular embodiments disclosed, apparatus for guiding two yarns over a curved surface is combined with a yarn drawing machine including feed rollers, take-up rollers and an intermediate cylindrical stretching element, thereby permitting two yarns to be drawn at the same drawing station. One or a pair of guide arms, each having a guide opening for a yarn at either end, are arranged relative to the cylindrical element to pass the yarns over the element in two spaced planes. The arms and the cylindrical element are pivotable one relative to the other to shift, e.g., interchange, the loci of the yarns on the element. In one embodiment, the guide arms are pivoted while the cylindrical element is held stationary, and in another the cylindrical element is pivoted while the arms remain fixed. Where a pair of guide arms are used, they may be placed on opposite sides of the cylindrical element to guide the yarns in their approach to and departure from the cylindrical element.

United States Patent 91 Marchand [451 Feb.12, 1974 YARN GUIDINGAPPARATUS Andre M. Marchand, Roanne, France [75] Inventor:

[73] Assignee: Ateliers Roannais De Constructions Textiles, Roanne(Loire), France 22 Filed: Sept. 12, 1972 21 Appl. No.: 288,417

[30] Foreign Application Priority Data Primary Examiner-Louis K. RimrodtAttorney, Agent, or Firm-Brumbaugh, Graves, Donohue & Raymond [57]ABSTRACT In the particular embodiments disclosed, apparatus for guidingtwo yarns over a curved surface is combined with a yarn drawing machineincluding feed rollers, take-up rollers and an intermediate cylindricalstretching element, thereby permitting two yarns to be drawn at the samedrawing station. One or a pair of guide arms, each having a guideopening for a yarn at either end, are arranged relative to thecylindrical element to pass the yarns over the element in two spacedplanes. The arms and the cylindrical element are pivotable one relativeto the other to shift, e.g., interchange, the loci of the yarns on theelement. In one embodiment, the guide arms are pivoted while thecylindrical element is held stationary, and in another the cylindricalelement is pivoted while the arms remain fixed. Where a pair of guidearms are used, they may be placed on opposite sides of the cylindricalelement to guide the yarns in their approach to and departure from thecylindrical element.

19 Claims, 5 Drawing Figures Patented Feb. 12, 1974 D 3,790,996

2 Sheets-Sheet l FIG.

Patented Feb. 12, 1974 2 Sheets-Sheet 2 A 1 YARN GUIDING APPARATUSBACKGROUND OF THE INVENTION The present invention relates generally toapparatus for passing two yarns over an element having a curved surfaceand, more particularly, to guiding apparatus for drawing syntheticyarns.

Although the invention is illustrated and described herein by referenceto a machine for drawing synthetic yarn, and specifically one includinga cylindrical drawing element, it goes without saying that the inventionis in no way limited to this embodiment or use, but thatit also hasapplication to all devices formed by at least one curved element overwhich it is desired to pass two yarns in parallel, whether or not theyarns are to be subjected to a particular treatment.

It is known that in order to give a synthetic yarn its mechanicalcharacteristics, it must be subjected, in succession, after spinning andextrusion, to a stretching or drawing operation which has the effect oforienting the molecules of which the yarn is composed. This operation isgenerally carried out between two devices which draw the yarn, thedifference in speed of which is adjusted as a function of the extent towhich it is desired to stretch the yarn. In practice, especially withpolyamide yarns, between these two drawing devices, the yarn engagesmost frequently on a fixed rod, which may. or may not be heated,sometimes called the stretching finger, around which it makes one ormore turns.

It is also known to insert, between the drawing devices, a heatingelement of suitable shape over which the moving yarn passes. Finally,one of the drawing devices can be a rotating heating cylinder of themultiturn type, equipped with a return roller, the yarn making one ormore turns around the combination of heating cylinder and return roller.

In order to increase the profitability of stretching machines, it hasbeen proposed to treat several yarns simultaneously at the samestretching station. However, if, during the operation, one of the yarnsbreaks, this method has numerous disadvantages which make itinapplicable in industry.

If, for example, the yarn which breaks is the one situated at the frontor outside location, that is to say that which passes in the planesituated nearest to the free end of the cylinder, it is sufficient torestart this yarn, taking care obviously to avoid it affecting thepassage of the other yarn. On the other hand, if it is the yarn situatedat the back or inside which breaks, difficulties are encountered:firstly, this broken yarn presents the risk of becoming entangled withits neighbours and thus of causing the whole lot to-break; and secondly,and most importantly, it is necessary to stop the whole unit in order toproceed with repairs and a new start. These and other disadvantages ofthe prior art are overcome by the present invention.

SUMMARY OF THE INVENTION Generally, the present invention relates toapparatus for passing two yarns over one and the same curved, e.g.,cylindrical, element, which may or may not rotate, in which, in the caseof breakage of one of the two yarns, it is not necessary to stop theunit to remove and restart the yarn which broke.

A representative embodiment constructed in accordance with the inventionincludes'a cylindrical component over which two yarns pass in twoparallel planes, which planes are substantially perpendicular to theaxis of the cylindrical component, and at least one guide arm carryingat both of its ends a means of guiding each of the two yarns. The guidearm is positioned in such a way that the two parallel planes of thecylinder in which the yarns pass, i.e., the planes generally containingthe yarns as they pass over the cylinder, are spaced apart relative toone another along the axis of the cylinder, and such that each yarn ispresented tangentially on either side of the cylinder. The device ischaracterized further in that the cylindrical component and the guidearm can pivot relative to one another about the same axis to shift theloci of the yarns on the cylindrical component.

In practice, the guide arm and the cylindrical component preferablypivot about an axis formed by the intersection of the plane in which theyarns lie as they approach the cylindrical component with the planewhich passes through the axis of the cylinder in a direction parallel tothe direction of forward movement of the yarns.

In one embodiment, the invention includes two pivotally mounted guidearms which are parallel and located on either side of the cylinder,preferably symmetrically. In this way, each yarn is guided before andafter its passage over the cylinder, which makes it easier to positionthe yarn. Significant advantages over the prior art are also realized,however, if only one guide arm is employed.

In a first advantageous embodiment, it is the guide arm or arms carryingthe yarn guides at their ends which pivot. As already stated, thecylindrical element can be a cylinder forming the engagement componentof a machine for drawing synthetic yarns, and may be either fixed orrotatable and heated or unheated. In this way, it is possible to use asingle stretching finger for two yarns.

If, during operation, one of the yarns breaks and if this yarn is theone which passes on the inside or back, it is sufficient to pivot theguide arms to the other extreme position and thus to shift the yarn atthe front into the position at the back, and then to carry out therestarting of the broken yarn which is now in the position at the front.If subsequently the yarn situated on the inside breaks again, the sameprocedure is repeated. Thus, since the position of each of the two yarnson the cylinder can be varied alternately and instantaneously from theposition at the front to the position at the back, without having tostop the machine, a troublesome problem of the prior art has been solvedin a simple, effective and economical way. This makes it possibleconsiderably to improve the yield of drawing machines and enablesconventional drawing machines to be readily and inexpensively modifiedin accordance with the invention.

In a second embodiment, the guide arm or arms are fixed and thecylinder'pivots about the axis formed by the intersection of the planein which the yarns pass with the plane passing through the axis of thecylinder in a direction parallel to the direction of forward movement ofthe yarns. This embodiment makes it possible to keep the yarns in afixed position relative to the delivering elements and thus to haveconstantengagements on the yarns.

BRIEF DESCRIPTION OF THE DRAWINGS The invention and the advantages whichresult from it will be better understood from the following description,with reference to the attached figures, in which:

FIG. 1 represents a perspective view of an embodiment of the invention,with pivoting arms;

FIG. 2 is a horizontal view of the embodiment of FIG. 1, taken along theline 2-2;

FIG. 3 is a perspective view of a second embodiment according to theinvention, with a pivoting cylinder; and

FIGS. 4A and 4B are partial horizontal views taken along the line 44 ofFIG. 3, with parts omitted for clarity.

DESCRIPTION OF EXEMPLARY EMBODIMENTS In the embodiment illustrated inFIG. 1, a cylinder 10, which may be fixed or may be able to rotate andwhich may or may not be heated, is mounted, by means of a shaft 12, on agenerally U-shaped member 14. The member 14 is supported in the axis ofthe cylinder by a cross bar 16 of a frame (not shown) of a conventionalmachine for drawing synthetic yarns. The arms 18 and 20 of the U-shapedmember 14 are situated in a vertical plane passing through the axis ofthe cylinder 10 and are respectively placed so that one 18 is above thecylinder and the other 20 below. Close to their free ends, the arms 18and 20 carry two pivoting pins 22 and 24 which are aligned in the samevertical plane.

Another generally U-shaped member 26 is positioned outside the U-shapedmember 14, relative to the cylinder, and possesses two arms 28 and 30.The arms 28 and 30 are pivotally mounted on the pins 22 and 24,respectively. In this way, the outer U-shaped member 26 can pivotrelative to the inner U-shaped member 14, which is rigidly fixed to thecross bar 16 of the frame. The upper arm 28 of member 26 is firmly fixedto a double yarn guide arm 32. The lower arm 30 is similarly fixed toanother double yarn guide arm 34 which is identical to the first. In thecase of the guide arm 32, the yarns 36 and 38 pass through two openeyelet-holes 40 and 42, of suitable shape and nature, situated at therespective ends of the arm 32. Likewise, in the case of the guide arm34, the yarns pass through two open eyelet-holes 44 and 46. Preferably,the guide arms 32 and 34 are so arranged that the eyelet-holes 40 and44, on the one hand, and the eyelet-holes 42 and 46, on the other, arevertically above one another.

As a result of the pins 22 and 24 being aligned vertically, the inleteyelet-hole 40, 42 and outlet eyelet-hole 44, 46 for each yarn 36, 38also remain vertically aligned throughout in relation to the cylinder 10when-.

ever the outer U-shaped member 26 pivots and conjointly moves the yarnguide arms 32 and 34.

In the two directions of pivoting which can be applied to the U-shapedmember 26, the member comes to rest against the cross bar 16, thusdefining two stable positions which are symmetric relative to the axisof the cylinder l0. In one of these stable positions of the member 26(shown in full lines in FIG. 2), the eyelet-holes 40 and 44 define thepassage at the front for one yarn 36, whilst the eyelet-holes 42 and 46define the passage at the back for the other yarn 38, as seen by anoperator looking straight at the cylinder 10 from the left hand side ofFIG. 1.

In the other stable resting position of the U-shaped member 26 (shown inphamtom in FIG. 2), the yarn 36 which passes through the eyelet-holes 40and 44 assumes a path at the back and the yarn 38 of eyeletholes 42 and46 assumes a path at the front.

In order to hold the U-shaped member 26 in one or the other of its tworesting positions, the upper arm 28 carries a pivot pin 48 which ispivotally engaged by collar 50 attached to one end of a rod 52. Theopposite end of the rod 52 passes through an opening in a bar 54 whichis firmly fixed to the frame (not shown) of the machine. A compressionspring 56 is positioned over the rod 52 and bears against the collar 50at one end and a detent 58 at the other. The detent is suitablyapertured to slidingly receive the rod 52 and, on the side thereoffacing the bar 54, is formed with a generally spherically-shaped bearingsurface. (See FIG. 2) The opening in bar 54 through which the rod 52passes is correspondingly shaped to provide a spherical seat for thedetent 58.

It will be appreciated that, once moved to one of its rest positions,the U-shaped member 26 will be retained in that position by the force ofthe spring 56. Thus by shifting the U-shaped member 26 either to theright or to the left (as viewed in FIG. 1), using for this purpose theforwardly extending part of arm 28, the operator can, at will, reverse,i.e., shift from the front to the back and vice versa, the paths of theyarns 36 and 38 on the cylinder 10.

When the machine illustrated in FIGS. 1 and 2 is started up, the yarn 38drawn by the drawing unit, or feed rollers, 60 is inserted into theeyelet-hole 42 situated at the back. The operator causes it to make oneor more turns on the cylinder 10 in the clockwise direction, and theninserts the yarn at the outlet into the eyelet-hole 46 which is directlybelow the hole 42. The yarn 38 is then drawn by the drawing unit, ortake-up rollers, 62, the controlled speed of which is greater than thatof the unit 60 and in a ratio such as to cause the desired stretching ordrawing of the yarn. Likewise, the yarn 36 drawn by the drawing unit, orfeed rollers, 64 is passed through the eyelet-hole 40 situated at thefront. The operator causes it to make one or more turns on the cylinder10 in the anti-clockwise direction and inserts the yarn at the outletinto the eyelet-hole 44 which is directly below eyelet-hole 40. The yarn36 is then drawn by the unit, or takeup rollers, 66, the controlledspeed of which is also greater than that of the unit 64 to causestretching of the yarn.

Preferably, the upper feed units 60 and 64 are driven at the same speed,and the take-up units 62 and 66 are driven at the same faster speed, soas to stretch the two yarns in the same ratio.

If the yarn 38 placed at the back of the cylinder 10, relative to theyarn 36, breaks, the operator pivots the U-shaped member 26. The turn orturns of the yarn 36 placed at the front of the cylinder 10 slidetowards the back and take up the position which those of the yarn 38occupied before the breakage. The eyelet-holes 42 and 46 come to thefront during pivoting of the member 26 and it suffices to restart theyarn 38 as explained above. The turn or turns of the yarn 38 then takeup the position on the cylinder 10 which the turn or turns of the yarn36 occupied previously.

FIGS. 3, 4A and 4B illustrate another embodiment of the invention, thistime with a pivoting cylinder. Like components are indicated by likeprimed numbers and, except as otherwise noted, will be understood tofunction in the same manner as in the embodiment of FIGS. 1 and 2. I

Here, the guide arms 32' and 34, carrying at their ends the eyelet-holes4046' for guiding the yarns 36 and 38, are fixed, i.e., the U-shapedmember 26' is rigidly attached to the cross bar 16', and the cylinderIt) is arranged to pivot about the axis formed by the intersection ofthe plane in which the yarns 36' and 38' lie and the plane which passesthrough the axis of the cylinder parallel to the direction of forwardmovement of the yarns.

As one suitable arrangement for pivoting the cylinder 10, the innerU-shaped member 14' is pivotally supported within the outer U-shapedmember 26 by means of the pins 22' and 24. It is moved between its restpositions (illustrated respectively in full lines in FIGS. 4A and 4B) inorder to bring the eyelet-holes 40 and 44 and yarn 36', on the one hand(FIG. 4A), or eyelet-holes 42' and 46 and yarn 38, on the other (FIG.4B), to the front. If desired, one of the arms 18 and of the U-shapedmember 14' may be extended in the forward direction to facilitatepivoting of the member 14', and hence of the cylinder 10', by theoperator.

" Conveniently, the cylinder 10' may be positioned at its rest positionsby stops 68 and 70 (FIG. 3) carried by the cross bar 16'. The rod 52'may thus extend through an opening in the U-shaped member 26', whichserves as a seat for the spherically-shaped detent 58. As before, acompression spring 56' is constrained between the detent 58' and acollar 50' fixed to the opposite end of the rod 52'. The collar 50 maybe pivotally secured to the upper arm 18' of the U-shaped member 14' bya pivot pin 48', so that the spring 58 urges the member 14' against thestops 68 and 70 to hold the cylinder 10' in the proper rest positions.

The yarns 36' and 38' are drawn by the drawing units 60'-66' and passedthrough the eyelet-holes 40'-46 and around the cylinder 10 in the samemanner as in the embodiment of FIGS. 1 and 2. They are likewiserestarted if broken in the same manner as previously explained, except,of course, that the cylinder 10 rather than the outer U-shaped member 26is pivoted to move the broken back yarn to the front position.

In a practical procedure, and whatever the embodimentenvisaged, the yarnguides situated at the end of the guide arms preferably are driven inconventional fashion with a slight secondary reciprocating movement in asubstantially perpendicular plane relative to the direction of forwardmovement of the yarns. This is done in order to avoid wear of thecylinder in one spot and to minimize abrasion of the yarns.

As already stated, apparatus constructed according to the invention isparticularly advantageous for stretching synthetic yarns because,without excessive alteration of existing material and by means of anapparatus which is simple to construct and easy to use, it is possibleto treat two yarns simultaneously at a single drawing station and thusconsiderably to decrease the investment in future installations and toincrease the profitability of those already in existence.

It goes without saying that this device can be used for other purposesthan stretching synthetic yarns without going outside the scope of thepresent invention. For example, it can be used successfully with anytype of treatment which is applied to yarns of any nature, and in whichone or two yarns are passed over at least one curved surface which mayor may not be rotated and which may or may not be heated. All suchmodifications and variations of the invention, and of the particularembodimentsdescribed above, are therefor encompassed within the spiritand scope of the appended claims.

I claim:

1. Apparatus for simultaneously drawing two yarns comprising meansforming a curved surface over which the yarns are to be passed, feedrollers for feeding the yarns to the curved surface, take-up rollers fortaking up the yarns after their passage over the curved surface, thetake-up rollers being driven faster than the feed rollers so as to drawthe yarns by a desired amount, each of the yarns engaging the curvedsurface and being disposed substantially in a plane, the two planescontaining the yarns being spaced apart from each other, means forguiding the first yarn, means for guiding the second yarn, and means forshifting the relative positions of the curved surface-forming means andthe first and second guide means so as to shift the loci of the firstand second yarns on the curved surface.

2. Apparatus according to claim 1 in which each of the first and secondguide means includes a pair of spaced yarn guiding elements, the pairedguide elements being disposed on opposite sides of the curved surfaceforming means.

3. Apparatus according to claim 1 in which the shifting meanssimultaneously shifts the relative positions of the curved surfaceforming means and the first and second guide means so as to reverse theloci of the first and second yarns on the curved surface.

4. Apparatus according to claim 3 in which the curved surface is acylindrical surface, the curved surface forming means is cylinder means,and the two planes containing the two yarns are substantiallyperpendicular to the axis of the cylinder means.

5. Apparatus according to claim 4 in which the cylinder means is mountedto prevent pivoting about'an axis perpendicular to the axis of thecylinder means, and the shifting means shifts the first and second guidemeans in generally opposite directions.

3. Apparatus according to claim 7 in which the shifting means comprisesa generally U-shaped member disposed with the arms thereof on oppositesides of the cylinder means and pivoted for rotation about the same axisas the first and second guide means-carrying arms, the first and secondguide means-carrying arms being mounted on the respective arms of theU-shaped member for rotation therewith.

9. Apparatus according to claim 8 in which the shifting means furthercomprises means for releasably holding the U-shaped member, and thus theguide meanscarrying arms, in two rotational positions relative to thecylinder means, each rotational position corresponding to particularloci of the first and second yarns on the cylinder means, whereby uponpivoting of the U- shaped member from one rotational position to theother the loci of the first and second yarns on the cylinder means arereversed.

10. Apparatus according to claim 9 in which the shifting means furthercomprises a second generally U- shaped member disposed within the firstU-shaped member, means carried by the second U-shaped member forsupporting the cylinder means between the arms thereof, means supportingthe second U-shaped member so as to prevent pivoting thereof about anaxis perpendicular to the axis of the cylinder means, and means carriedby the arms of the second U-shaped member for pivotally supportingthereon the first U- shaped member.

11. Apparatus according to claim 10 further comprising first and secondfeed rollers for feeding the first and second yarns to the cylindermeans and first and second take-up rollers for taking up the first andsecond yarns after their passage over the cylinder means.

12. Apparatus according to claim 4 in which the first and second guidemeans are mounted to prevent pivoting about an axis perpendicular to theaxis of the cylinder means, and the shifting means shifts the cylindermeans in generally opposite directions.

13. Apparatus according to claim 12 in which the first and second guidemeans are disposed at least in part at opposite ends of an arm fixedagainst rotation about an axis substantially perpendicular to the axisof the cylinder means.

14. Apparatus according to claim 13 in which the first and second guidemeans are further disposed at opposite ends of a second arm fixedagainst rotation about an axis substantially perpendicular to the axisof the cylinder means, and the first and second arms are disposed onopposite sides of the cylinder means.

15. Apparatus according to claim 14 in which the shifting meanscomprises a generally U-shaped member disposed with the arms thereof onopposite sides of the cylinder means and pivoted for rotation about anaxis substantially perpendicular to the axis of the cylinder means, andmeans carried by the U-shaped member for supporting the cylinder meansfor rotation therewith.

16. Apparatus according to claim 15 in which the shifting means furthercomprises means for releasably holding the U-shaped member, and thus thecylinder means, in two rotational positions relative to the guidemeans-carrying arms, each rotational position corresponding toparticular loci of the first and second yarns on the cylinder means,whereby upon pivoting of the U-shaped member from one rotationalposition to the other the loci of the first and second yarns on thecylinder means are reversed.

17. Apparatus according to claim 16 in which the shifting means furthercomprises a second generally U- shaped member disposed around the firstU-shaped member, the arms of the second U-shaped member carrying thefirst and second guide means-carrying arms, means supporting the secondU-shaped member so as to prevent pivoting thereof about an axisperpendicular to the axis of the cylinder means, and means carried bythe arms of the second U-shaped member for pivotally supporting thereonthe first U-shaped member.

18. Apparatus accoring to claim 1 in which the curved surface-formingmeans is heated.

19 Apparatus according to claim 1 in which the curved surface-formingmeans is mounted for rotation about an axis substantially perpendicularto the planes containing the two yarns.

1. Apparatus for simultaneously drawing two yarns comprising meansforming a curved surface over which the yarns are to be passed, feedrollers for feeding the yarns to the curved surface, take-up rollers fortaking up the yarns after their passage over the curved surface, thetake-up rollers being driven faster than the feed rollers so as to drawthe yarns by a desired amount, each of the yarns engaging the curvedsurface and being disposed substantially in a plane, the two planescontaining the yarns being spaced apart from each other, means forguiding the first yarn, means for guiding the second yarn, and means forshifting the relative positions of the curved surface-forming means andthe first and second guide means so as to shift the loci of the firstand second yarns on the curved surface.
 2. Apparatus according to claim1 in which each of the first and second guide means includes a pair ofspaced yarn guiding elements, the paired guide elements Being disposedon opposite sides of the curved surface forming means.
 3. Apparatusaccording to claim 1 in which the shifting means simultaneously shiftsthe relative positions of the curved surface forming means and the firstand second guide means so as to reverse the loci of the first and secondyarns on the curved surface.
 4. Apparatus according to claim 3 in whichthe curved surface is a cylindrical surface, the curved surface formingmeans is cylinder means, and the two planes containing the two yarns aresubstantially perpendicular to the axis of the cylinder means. 5.Apparatus according to claim 4 in which the cylinder means is mounted toprevent pivoting about an axis perpendicular to the axis of the cylindermeans, and the shifting means shifts the first and second guide means ingenerally opposite directions.
 6. Apparatus according to claim 5 inwhich the first and second guide means are disposed at least in part atopposite ends of an arm pivoted for rotation about an axis substantiallyperpendicular to the axis of the cylinder means.
 7. Apparatus accordingto claim 6 in which the first and second guide means are furtherdisposed at opposite ends of a second arm pivoted for rotation about thesame axis of the first arm, and the first and second arms are disposedon opposite sides of the cylinder means.
 8. Apparatus according to claim7 in which the shifting means comprises a generally U-shaped memberdisposed with the arms thereof on opposite sides of the cylinder meansand pivoted for rotation about the same axis as the first and secondguide means-carrying arms, the first and second guide means-carryingarms being mounted on the respective arms of the U-shaped member forrotation therewith.
 9. Apparatus according to claim 8 in which theshifting means further comprises means for releasably holding theU-shaped member, and thus the guide means-carrying arms, in tworotational positions relative to the cylinder means, each rotationalposition corresponding to particular loci of the first and second yarnson the cylinder means, whereby upon pivoting of the U-shaped member fromone rotational position to the other the loci of the first and secondyarns on the cylinder means are reversed.
 10. Apparatus according toclaim 9 in which the shifting means further comprises a second generallyU-shaped member disposed within the first U-shaped member, means carriedby the second U-shaped member for supporting the cylinder means betweenthe arms thereof, means supporting the second U-shaped member so as toprevent pivoting thereof about an axis perpendicular to the axis of thecylinder means, and means carried by the arms of the second U-shapedmember for pivotally supporting thereon the first U-shaped member. 11.Apparatus according to claim 10 further comprising first and second feedrollers for feeding the first and second yarns to the cylinder means andfirst and second take-up rollers for taking up the first and secondyarns after their passage over the cylinder means.
 12. Apparatusaccording to claim 4 in which the first and second guide means aremounted to prevent pivoting about an axis perpendicular to the axis ofthe cylinder means, and the shifting means shifts the cylinder means ingenerally opposite directions.
 13. Apparatus according to claim 12 inwhich the first and second guide means are disposed at least in part atopposite ends of an arm fixed against rotation about an axissubstantially perpendicular to the axis of the cylinder means. 14.Apparatus according to claim 13 in which the first and second guidemeans are further disposed at opposite ends of a second arm fixedagainst rotation about an axis substantially perpendicular to the axisof the cylinder means, and the first and second arms are disposed onopposite sides of the cylinder means.
 15. Apparatus according to claim14 in which the shifting means comprises a generally U-shaped memberdisposed with the arms thereof on opposite sides of the cylinder meansand pivoted for rotation about an axis substantially perpendicular tothe axis of the cylinder means, and means carried by the U-shaped memberfor supporting the cylinder means for rotation therewith.
 16. Apparatusaccording to claim 15 in which the shifting means further comprisesmeans for releasably holding the U-shaped member, and thus the cylindermeans, in two rotational positions relative to the guide means-carryingarms, each rotational position corresponding to particular loci of thefirst and second yarns on the cylinder means, whereby upon pivoting ofthe U-shaped member from one rotational position to the other the lociof the first and second yarns on the cylinder means are reversed. 17.Apparatus according to claim 16 in which the shifting means furthercomprises a second generally U-shaped member disposed around the firstU-shaped member, the arms of the second U-shaped member carrying thefirst and second guide means-carrying arms, means supporting the secondU-shaped member so as to prevent pivoting thereof about an axisperpendicular to the axis of the cylinder means, and means carried bythe arms of the second U-shaped member for pivotally supporting thereonthe first U-shaped member.
 18. Apparatus accoring to claim 1 in whichthe curved surface-forming means is heated. 19 Apparatus according toclaim 1 in which the curved surface-forming means is mounted forrotation about an axis substantially perpendicular to the planescontaining the two yarns.